Blow molding parisons using fluid sealing



NOV. 18, 1969 N WILS ET AL 3,479,420

BLOW MOLDING PARISONS USING FLUID SEALING Filed May 29, 1967 mmcfwwm 4 mmux fi M N f Em WW 4 WA a M 7 3 9 H M \L 9 m \/.WK2 3 m A E 2 4 m f 3 92 Q 2 w 4 7 F H w A h 5 1 J a United States Patent 3,479,420 BLOWMOLDING PARISONS USING FLUID SEALING Newton R. Wilson and Thomas J.Nave, Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of Delaware FiledMay 29, 1967, Ser. No. 641,812 Int. Cl. B29d 23/03 US. Cl. 264-89 6Claims ABSTRACT OF THE DISCLOSURE An open ended parison to be molded isclosed adjacent its open end by use of at least one fluid stream.

This invention relates to a new and improved method for molding plasticparisons as formed.

Heretofore a hollow, highly heated tube of plastic (parison) has beenclamped between two mold halves and air introduced into the hollowinterior thereof to expand same outwardly to conform with the interiorconfiguration of the mold halves thereby forming a molded article.Parisons are usually formed continuously and after a certainpredetermined length of parison has been formed the mold halves areclosed thereabout and the blow molding operation carried out.

Because the parison is in a highly heated state before it is molded thesides of the parison tend to stick to one another when brought intocontact and, therefore, it is desirable to make sure that the parisondoes not collapse to any degree before the molding operation. It isoften desirable to partially inflate the parison before molding so thata molded article having a uniform wall thickness can be formed. One wayof preventing collapsing of the heated parison is to introduced apressurized fluid such as air into the interior of that parison.However, to preblow the parison it is necessary to close the open endthereof to prevent escape of the pressurized fluid. In some instances itis desirable to direct the parison to one side of a mold containingslidable inserts to insure that a portion is pinched out to formhandles, etc.

It is diflicult to close the open end of the parison without undulycooling at least some portion of the parison that is to be subsequentlyblow molded, undue cooling causing undue thickening of the cooledportion with undue thinning of adjacent hotter areas during blow moldingthereby providing a molded article of a nonuniform wall thickness. Itwas heretofore thought to be particularly difficult to use any meansclosely related to what was considered in the art to be cooling devicesand therefore the use of fluid streams was heretofore thought not to besuitable for such operations.

It has now been found that a heated parison can be closed as to its openend using a fluid stream if the fluid stream is directed against anexternal portion of the heated parison adjacent the open end so as tocollapse the parison sides against one another while the mold halves aremoved towards one another to clamp about the parison for subsequentmolding of same. To prevent undue cooling, it is important to use thefluid stream only while the mold halves are moved towards one another.By this particular method it has been found that the open end of theparison is satisfactorily sealed for the introduction of the pressurizedfluid into the interior thereof without unduly cooling portions of theheated parison that are to be subsequently molded. The fluid streamitself is directed primarily toward a portion of the heated parisonwhich is adjacent the open end and which is normally almost completelytrimmed from the final molded article as scrap so that cooling of thatportion does not susbtantially affect the wall thickness of the moldedarticle.

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Also according to this invention there is described apparatus forclosing the open end of a heated parison that is to be molded betweenmold halves wherein at least one mold half carries fluid spray means ina manner such that fluid sprayed therefrom is directed towards apredetermined area relative to the opposing mold half, i.e. the areacorresponding to the area of the mold half where the spray means iscarried, and means is provided for admitting the fluid under pressure toboth said spray means and the interior of the parison when said moldhalves are moved towards one another.

The method of this invention is useful for making a wide variety ofmolded plastic articles such as bottles, bottle carriers, tote boxes,and the like.

Accordingly, it is an object of this invention to provide a new andimproved method for forming molded plastic articles. A particular objectof this invention is to provide a new and improved method for blowmolding plastic parisons.

Other aspects, objects and the several advantages of the invention willbe apparent to those skilled in the art from the following descriptionand the appended claims.

In the drawings, FIGURE 1 shows the system embodying the invention.

FIGURES 2 and 3 show embodiments of the invention different from that ofFIGURE 1.

In FIGURE 1, there is shown an extruder die 1 from which is issuing ahollow, heated, cylindrical, parison 2. Parison 2 issues downwardlybetween spaced apart mold halves 3 and 4. Die 1 is operatively connectedthrough conduit 5 to an accumulator 6 which has a piston 7 thereinconnected to supporting rod 8 which extends exteriorly thereof. Thematerial from which the parison is formed is supplied to accumulator 6from a conventional extruder 9 (not completely shown) through conduit10.

Mold halves 3 and 4 are movable towards and away from one another byconventional power means (not shown) which is connected to rods 15 and16.

Mold 3 carries on the bottom edge thereof a hollow cylinder 17 which isopen at one end and slidably carries piston 18 in that open end. Piston18 is resiliently biased towards mold 4 when molds 3 and 4 are in aspaced apart relation as shown in the drawing by way of resilient means19 which can be a coiled spring or similiarly functioning knownapparatus.

Arm 20 extends downwardly from mold 3 so as to contact trip arm 21 ofrnicroswitch 22 when mold 3 is moved towards molds 4 at the beginning ofthe blow molding operation. Thus, when mold halves 3 and 4 are movedtowards one another to clamp parison 2 for blow molding thereof, switch22 is actuated at the start of movement of the mold halves.

Mold half 4 carries on the bottom side thereof hollow member 23 whichhas an opening 24 in the side thereof which faces the area on mold half3, i.e. piston 18. The height of opening 24 varies from 1 or 2 mils upto a quarter of an inch or more and is of a Width which is substantiallythe same as the width of mold 4 when looking directly into cavity 25 ofthat mold from the position of mold half 3. Piston 18 can have a widthsubstantially the same as that of opening 24.

Microswitch 22 is operatively connected in a conventional manner by wayof a wire or wires 26 to a conventional, normally closed solenoid valve27. Valve 27 is operatively connected to conduit 28 which is connectedto a source of fluid under pressure and also to fluid spray means 23 byway of stretchable conduit 29. Stretchable conduit 29 can be anyconventional material such as coiled rubber tubing. Conduit 2-8 is alsoconnected to conduit 30 which in turn is connected to conduit 31.Conduit 31 supplies fluid under pressure through die head 1 and into thehollow interior of parison 2. Supplementary fluid under pressure can besupplied to the system by way of conduit 32.

Supplementary air conduit 32 is normally used to admit higher pressuredfluid to the interior of parison 2 after mold halves 3 and 4 haveclamped. This fluid is used to force the clamped parison out against theinterior surfaces of mold halves 3 and 4 thereby forming the moldedarticle.

Normally, supplementary fluid is desirably supplied only 'to conduit 31so that, if it is desired to conserve the fluid in conduit 32, conduitcan be closed at or before the fluid in conduit 32 is passed intoconduit 31 but at or after mold halves 3 and 4 have clamped aroundparison 2. This can be accomplished by mounting a normally closedsolenoid valve in conduit 30 and operably connecting the same by a wireor wires to switch 22 so that both valves 27 and 35 are opened by theactuation of switch 22. In addition, valve 35 is operably connected to aconventional timer means 37 by way of a wire or wires 38, which timermeans is set to allow valve 35 to stay open for only a predeterminedlength of time. Thus, after timer 37 times out valve 35 is closed whilevalve 27 stays open. Thereafter, when higher pressure fluid in conduit32 is passed into conduit 31 this fluid is stopped in conduit 30 byclosed valve 35.

It should be noted that the use of valve 35 is not necessary to theoperation of the invention but can be desirable in order to conserve thehigh pressure fluid in conduit' 32 since this fluid is not usuallynecessary for use in spray 23 but is necessary for the actual blowmolding of parison 2.

FIGURE 2 shows an embodiment of the invention wherein the minimum amountof parison is Wasted by mounting the spray outlet 24 and opposing piston18 as close as possible to the bottom surfaces of the mold cavities inmold halves 3 and 4 without structurally weakening the mold halves. Bythis embodiment wherein the spray means and opposing piston 18 aremounted directly in the mold halves themselves, the parison need notextend below the bottom surfaces of the mold halves and this amount ofparison material is conserved thereby reducing the waste materialtrimmed from the molded article.

FIGURE 3 shows an embodiment of the invention wherein opposing spraymeans are carried by mold halves 3 and 4 and aligned so that they sprayfluid received from lines 29 directly at the orifices of one anotherthereby obviating the need for piston 18. Since the fluid streams fromboth spray means should meet one another in order to properly collapsethe parison, it is desirable to mount both spray means on the moldhalves with adjustable fixing means so that each spray means can bevaried in a vertical plane to obtain the exact alignment desired.Adjustable means 40 can be any conventional device such as aconventional thumb screw.

In operation, in FIGURE 1, mold halves 3 and 4 are in their normalspaced apart relationship while a predetermined length of parison 2 ismelt extruded through die head 1. When the proper length of parison 2has been extruded, i.e. a portion thereof extends below the bottomsurfaces of mold halves 3 and 4, the parison extrusion is stopped orslowed and the mold halves are moved towards one another. As soon asmovement of the mold halves starts, switch 22 is actuated, therebyopening valve 27 and allowing pressurized fluid to pass through conduits28 and 29 into spray means 23 and out orifice 24 thereby impinging on alower portion of parison 2 adjacent the open end thereof and pushing theentire lower end of the parison towards collapse and towards piston 18.Eventually, piston 18 contacts the parison and the open end thereof iscollapsed by bringing opposite sides of the parison into contact withone another. Since the parison is still in the heated condition due tothe extrusion process it has just undergone, contacting of the interiorsurfaces of the parison under the pressure of the fluid stream emittedfrom spray 23 is suflicient to seal the open end of the parison.

While the open end of the parison is being sealed, fluid under pressureis being supplied "to the interior of the parison by way of conduit 31thereby positively preventing any premature collapsing of the parison inthe area of the parison which is to be subsequently blow molded. Inaddition, fluid supplied to the interior of the parison can be ofsufficient pressure to cause some preblowing of the parison if desired.After the mold halves 3 and 4 have clamped about parison 2 fluid under ahigher pressure than that supplied through conduit 28 is supplied toconduit 31 by way of conduit 32 to force parison 2 out against theinternal surfaces of mold halves 3 and 4 thereby forming a moldedarticle. Thereafter mold halves 3 and 4 are drawn away from one another,the molded article severed from the remainder of parison 2 and the cyclerepeated. W

This invention is applicable to substantially any formable plasticmaterial, especially thermoplastics. Generally, this invention appliesto homopolymers and copolymers formed from l-olefins having from 2-8carbon atoms per molecule, inclusive, polyamides, polyesters, polyvinylalcohol, acrylic polymers, polyvinyl chloride, polyvinyl acetate,polyvinylidene chloride, and the like, and mixures thereof.

The material from which the parison is formed should be heated to atemperature suflicient to cause portions of the parison to stick to oneanother when brought into contact with one another under slightpressure. Such temperatures are normally provided by the parison formingprocess such as the :melt extrusion process disclosed in FIGURE 1.However, if desired, additional heating of the parison can be provided,at least in the area of the open end which is to be collapsed so as toassure sealing of the open end on collapsing.

Generally, the parison should be heated to at least about the softeningpoint of the polymer from which the parison is made, the softening pointbeing determined in accordance with ASTM Dl52S58T. The term at leastabout the softening point is meant to includue temperatures up to 20 C.below the softening point since some materials such as polypropylene,upon cooling, remain sufficiently tacky to seal upon contact attemperatures up to 20 C. below their softening point. Generally,however, a polymer will be of a temperature of at least its softeningpoint when collapsed in accordance with the method of this invention.

The fluid under pressure utilized in either of conduits 28 or 32 can beany desirable fluid such as air, nitrogen, and the like and can bepreheated or at room temperature. The pressure of the fluid employed inconduits 28 through 31 will generally be in the range of from about 1 toabout 30 p.s.i.g. although higher or lower pressures can be useddepending upon the particular materials used to make the parison and thewall thickness of the'parison itself. The pressure of the fluid inconduit 32 will be that which is suflicient to blow mold the parison andwill generally be greater than the pressure of the fluid employed inconduit 28.

EXAMPLE Polyethylene having a density of 0.96 gram per cubic centimeterat 25 C. and a melt index of 0.2 is extruded at a temperature of about400 F. to produce a hollow, cylindrical parison using the apparatusshown in FIG- URE 1. The parison is continuously extruded through die 1until the lower, open end thereof extends between and below piston 18and orifice 24. Extrusion is stopped and molds 3 and 4 move towards oneanother and just as they start their movement towards one another switch22 is actuated thereby opening valve 27 and admitting air under pressureof 25 p.s.i.g. to the interior of spray means 23. After mold halves 3and 4 move into contact with and close about parison 2, air underpressure of p.s.i.g. is admitted to conduit 31 to blow mold that portionof the parison clamped between mold halves 3 and 4.

The 60 p.s.i.g. air is admitted to conduit 31 about 3 seconds aftervalve 27 is opened. Thus, if valve 35 is employed in conduit 30 andopened at the same time as valve 27 by way of the actuation of switch22, timer 37 will be set to time out in, 3 seconds at which time valve35 is closed so that valve 35 is closed at about the same time that thehigher pressure air is admitted to conduit 31.

Obvious variations and modifications of this invention can be made, orfollowed, in view of the foregoing, without departing from the spirit orscope thereof.

What is claimed is:

1. A method for closing the open end of a heated, hollow plastic parisoncomprising'forming said parison so as to pass between two spaced apartmold halves, said parison being heated to a temperature suflicient tocause portions thereof to stick to one another when brought intocontact, moving said mold halves towards one another to clamp saidparison therebetween after said parison has reached a predeterminedlength, while moving said mold halves towards one another directing astream of fluid under pressure from at least one mold half towards thecorresponding area of the opposing mold half and against an externalportion of said parison adjacent said open end so as to cause collapseof said open end thereby bringing opposing heated internal sides of saidparison in said collapsed portion into contact wth one another andintroducing fluid under pressure into the interior of said parisonswhile said mold halves are moved toward one another.

2. A method according to claim 1 wherein, said parison is formed from atleast one polymer selected from the group consisting of polymers ofl-olefins having from 2-8 carbon atoms per molecule, inclusive,polyamides, poly- 6 esters, polyvinyl alcohols, acrylic polymers,polyvinyl chloride, polyvinylidene chloride, and polyvinyl acetate, andmixtures thereof, and said parison is at a temperature while beingcollapsed of at least about the softening point of the polymer fromwhich the parison is made as determined by ASTM D-15255 8T.

3. The method according to claim 1 wherein said parison is formed bymelt extrusion.

4. The method according to claim 1 wherein said parison is formed bymelt extruding at least of a homopolymer and a copolymer each formedfrom l-olefins having 2-8 carbon atoms per molecule, inclusive, and saidparison while being collapsed is at a temperature of at least about thesoftening point of the polymer that forms the parison as determined byASTM D-152558T.

5. The method acocrding to claim 4 wherein said polymer is one ofpolyethylene, polypropylene, mixtures thereof, and copolymers ofethylene and propylene, and said fluid is air.

'6. The method acording to claim 1 wherein said parison while beingcollapsed is at a temperature of a least about the softening point ofthe polymer forming the parison as determined by ASTM D-1525-58T.

References Cited UNITED STATES PATENTS 2,690,592 10/1954 Schanz 18-143,239,402 3/1966 Ecklund 264172 XR 3,300,556 1/ 1967 Battenfeld 264983,311,684 3/1967 Heider 26499 ROBERT F. WHITE, Primary Examiner R. C.KUCIA, Assistant Examiner US. Cl. X.R.

